1. Field of the Invention
The present invention relates to resin boots for constant velocity universal joint used in a state of being firmly fixed to an outer peripheral surface of a tripod joint an outer periphery of which is formed in a concavo-convex shape, in a constant velocity universal joint, for example, used in a drive shaft and a propeller shaft for transmitting a power from an engine of a motor vehicle to a tire.
2. Prior Art
The tripod joint has recess portions formed in desired portions on the outer peripheral surface for various purposes comprising a thin forming, a weight saving and the like.
In the resin boots for constant velocity universal joint used in a state of being firmly fixed to the outer peripheral surface of the constant velocity universal joint, a bellows portion thereof plays a part in a cover and also a part in bending in correspondence to a motion of the drive shaft, the propeller shaft or the like, and an end portion thereof is firmly fixed to the outer periphery of the constant velocity universal joint via a band and plays a part in an oil (grease) seal and dust seal.
Accordingly, it is necessary to form an inner periphery of the end portion of the boots in a shape closely attached so as to be aligned with the outer periphery of the tripod joint (a joint outer race or the like), and since the tripod joint has the recess portion formed in the outer periphery thereof as described above, it is necessary that the end portion in a large diameter side firmly fixed to the outer periphery is formed in an inner peripheral shape having different thickness portions.
In conventional, as the boots for the constant velocity universal joint used in the tripod joint, there has been known a structure shown in FIG. 7 (for example, refer to non-patent document 1).
This conventional structure is constituted by a resin bellows 100 which is formed, for example, by an injection blow molding and has a uniform thickness in a large diameter side end portion 101, and a rubber grommet 200 which has an outer diameter fitted to an inner surface of the large diameter side end portion 101 of the resin bellows 100, is formed in a circular ring shape, and has thickness portions 201 protruding in an inner diameter direction every fixed intervals, is provided so as to fit an outer periphery of the grommet 200 independently formed as mentioned above to the inner periphery of the large diameter side end portion 101 of the bellows 100 and fit an inner periphery of the grommet 200 to an outer periphery of the tripod joint 80, and is fastened and firmly fixed to the outer periphery of the tripod joint 80 from the outer peripheral side of the large diameter side end portion 101 by a fastening device such as a band 300 or the like.
Further, there is a prior art document that a grommet and a bellows are integrally formed within a metal mold by previously forming a resin grommet having thickness portions protruding in an inner diameter direction every fixed intervals, holding the grommet within the metal mold and thereafter injection molding or blow molding the resin bellows (for example, refer to patent document 1 and patent document 2).
Non-patent document 1
Catalogue “Constant Velocity Universal Joints or Automobiles” (CAT. No. 5601-II/JE) page 9, issued on Feb. 3, 2000 by NTN Co., Ltd.
Patent document 1
Japanese Unexamined Utility Model Publication No. 2-22463
Patent document 2
Japanese Unexamined Patent Publication No. 2002-286048
However, as the structure described in FIG. 7, in accordance with the prior art mentioned above in which the bellows 100 and the grommet 200 are independently formed and are fitted and assembled, there is a problem in a grease leakage and an assembling operability. That is, if the fitting work is carelessly carried out at a time of fitting the grommet 200 to the inner periphery of the bellows large diameter side end portion 101, a displacement is generated between both elements. Further, it is possible to outward fit the bellows large diameter side end portion 101 after fitting the grommet 200 to the outer periphery of the tripod joint 80, however, there is a risk that the displacement is generated between the bellows large diameter side end portion 101 and the grommet 200, thereby generating the grease leakage, if the carelessness exists.
Further, in the prior art disclosed in patent document 1 or 2, since no specific technical means is provided in the portion in which the grommet and the bellows are integrally formed, both elements are not securely welded even if they are integrally formed on the surface. Accordingly, the portion which is expected to be integrally formed peels off, so that there is generated a problem such as the grease leakage or the like.
Accordingly, the inventors of the present application have paid attention to a dichroic molding, and have succeeded in developing a new useful method of secondarily forming a different thickness portion in the inner periphery of the large diameter side end portion of the resin bellows which is previously formed in accordance with a primary molding.